INTRODUCTION. 
8 
Crag” is a local term commonly applied in the east of 
England to any shelly marine sand. The word has been adopted 
by geologists as almost equivalent to Pliocene/' but it is never 
used for clays, such as the Chillesford Clay or Forest-bed. 
There is a great gap in Britain between the Pliocene strata 
and the next deposit below; for the Hamstead Beds (Middle 
Oligocene) yield a fauna of a totally different charaeter, having 
few, if any, of the species found in the strata above. The 
lapse of time denoted by this gap was so great that enormous 
masses of sediment were laid down in other districts during the 
interval. In Britain, though the intervening strata are absent, yet 
the great flexures in the south of England, and the thorough 
discordance between the Pliocene rocks and the underlying strata, 
serve to indicate how important the break really is. The move¬ 
ments in the south of England tilted the Oligocene deposits till 
they were vertical; but the oldest Pliocene strata seem to have 
been laid down when this folding had nearly ceased, and after 
denudation had removed the lower Tertiary groups. We thus 
find at Lenham Older Pliocene strata resting directly on the 
Chalk, and little, if at all, affected by the proximity of the Wealden 
anticline. 
The geographical distribution of our Pliocene deposits will best 
be understood by a reference to the Map at the commencement of 
this volume. Those of Older Pliocene age occupy a small area, being 
almost confined to the district around Orford, in Suffolk. Here 
the Coralline Crag occupies about 10 square miles. There are 
also small outliers at Eamsholt and Sutton, and a third, more 
distant, at Tattingstone, between Ipswich and Manningtree. All 
these localities are in the south-eastern part of the county of 
Suffolk. South of the Thames a small outlier of fossiliferous 
Lower Pliocene sands occurs on the edge of the North Downs, at 
Lenham. 10 miles east of Maidstone, and ironstones, probably of 
the same age, here and there cap the highest portion of the Down 
as far as Folkestone. One other small patch of Older Pliocene 
strata is found near the village of St. Erth, between St. Ives 
and Marazion, in Cornwall. There are also some curious sands 
at St. Agnes Beacon, on the north coast of Cornwall, which are 
probably of the same age, though, they have as yet yielded no 
fossils. 
Taking the whole of the fossiliferous Lower Pliocene deposits 
in Britain, and allowing for their probable extension under later 
formations in Suffolk, the total area occupied by them does not 
exceed 15 square miles. Even if we take into account all the 
deposits that can with any show of probability be referred to 
this period, such as the ironstone at Folkestone and the sands 
at St. Agnes Beacon, the area will not exceed 20 square miles. 
It is essential, however, to distinguish between the present 
limits of a formation and its original extension. The marine 
Older Pliocene strata evidently once extended far and wide over 
Britain, though they have now been reduced by denudation to 
such small and widely separated outliers. 
A 2 
